Soil-structure interaction of end-frames for high-speed railway bridges

Sammanfattning: In this thesis, the influence of soil-structure interaction (SSI) of end-frame bridges for high-speed railways was studied. Impedance functions, representing the SSI, was calculated and analyzed. The impedance functions were applied to end-frame bridge models which were analyzed for use in HSR. A new high-speed railway link is currently being planned in Sweden by the Swedish Transport Administration (Trafikverket). \textit{Ostl\"{a}nken} is planned to run between the cities of Stockholm and Link\"{o}ping with a maximum speed limit of 320km/h. As high-speed traffic induces high dynamic impact on bridges, dynamic analysis to ensure safety and passenger comfort is needed according to Eurocode. Thus, there is a demand of dynamically safe bridges that are also cost-effective. One cost-effective bridge is the soil integrated end-frame bridge, however, there are no design advice in Eurocode today on how to take SSI into consideration. The aim of the thesis has therefore been to investigate if the influence of SSI on end-frame bridges for HSR. This thesis was executed using the frequency domain approach to solve dynamic problems in finite element software. Furthermore, impedance functions have been obtained representing the SSI. Impedance functions take dynamic stiffness and dynamic damping into consideration where the damping consists of two parts: material damping and radiation damping due to energy dissipation in the form of elastic waves. To limit the model size, an absorbing region (AR) was used to mitigate waves originating from the source. The accuracy of impedance functions is dependent on several parameters and demands a great computational capacity to reach, mostly governed by the radiation condition. A parameter study of impedance functions was conducted, including parameters such as geometry, modulus of soil and detail levels. The impedance functions were then attached to bridge models on which trains modelled as moving point loads were applied. Envelopes of the acceleration and displacements have been presented and analyzed. Shear strain checks were made in order to verify the assumption of linear-elastic material behavior of the embankment. By using SSI in form of impedance functions attached to bridge models, numerical results show a great reduction of vibrations in models. The study suggests that a large end-frame, either long or high or both, may reduce acceleration as well as displacements. A stiffer embankment material may further reduce vibrations. Shear strain checks confirm that the assumption of linear-elastic soil behavior was true.